This invention relates to a process for patterning a polymer film by irradiation with light, a patterned polymer film produced by the process, and an organic electroluminescent device (hereinafter referred to as xe2x80x9corganic EL devicexe2x80x9d) comprising the patterned polymer film.
Hitherto, organic EL devices having a two-layer structure as shown in FIG. 1 in which a light-emitting layer 2 and a hole transport layer 3 in a layered structure, each comprising an organic compound, are placed between a metal cathode 1 and a transparent anode 4 formed on a transparent substrate 5, and organic EL devices having a three-layer structure as shown in FIG. 2 in which an electron transport layer 6, a light-emitting layer 2 and a hole transport layer 3 in a layered structure, each comprising an organic compound, are placed between a metal cathode 1 and a transparent anode 4 have been known. In the above device, the hole transport layer 3 has the function to facilitate the hole-injection from the anode and also to block electrons, and the electron transport layer 6 has the function to facilitate electron-injection from the cathode and also to block holes.
In these organic electroluminescent devices, ITO (indium tin oxide) is mainly used as a transparent electrode 4, and a film of ITO is formed on a glass substrate 5. By recombination of the electron injected from the metal cathode 1 and the positive hole injected into the light-emitting layer from the anode, light emitted in the process of a radiative decay of the produced exciton is taken out through the transparent anode and the transparent glass substrate.
The organic materials used in these organic EI devices include low molecular weight dyes, dyes dispersed in a polymer, conjugated type polymer materials, for example, so-called poly(arylenevinylene) polymers. Particularly, in recent years, the conjugated type polymer materials have been extensively studied due to their easy processing. These poly(arylenevinylene) polymers are utilized in organic EL devices in a single layer or in a layered structure combined with other electron transport layers. Details of organic electroluminenscence are described in, for example, the following literature references:
(1) xe2x80x9cOrganic EL Device Development Strategyxe2x80x9d, compiled by Next Generation Display Device Research Association, Science Forum (published 1992)
(2) xe2x80x9cElectroluminescent Materials, Devices, and Large-Screen Displaysxe2x80x9d, SPIE Proceedings Vol. 1910 (1993), E. M. Conwell and M. R. Miller.
In order to utilize an organic EL device using a poly(arylenevinylene) polymer film as a display such as a panel, patterning of the polymer film is required. For this purpose, a method for vapor-depositing an electrode pattern on the polymer film, and a method disclosed in WO92/03491 (International Publication No. Hei-6-501035) are known. The method disclosed in WO92/03491 comprises forming a film of an intermediate polymer of a conjugated type polymer, vapor-depositing a metal pattern on the polymer film, and converting the intermediate polymer into a conjugated polymer by heat treatment. In this method, since the acid generated by the heat treatment in a portion having the metal pattern is not easily removed from the film, a catalytic activity of the acid causes a difference in the conversion efficiency between the portion where there is no metal pattern and that where the polymer film is patterned.
However, in the method for patterning the above-described poly(arylenevinylene) polymer, it is complicated to vapor-deposit a metal pattern on the intermediate polymer and, depending upon the shape of patterns, a mask for vapor-deposition sometimes cannot be prepared. Thus, it has been desired to develop an easier method for patterning.
An object of the present invention is to provide a more expedient process for patterning a film of a poly(arylenevinylene) polymer.
Another object of the present invention is to provide a patterned film of the polymer produced by the process for patterning.
A further object of the present invention is to provide an organic EL device comprising the patterned film of the polymer.
The above objects can be achieved by the present invention hereinafter described in detail.
Generally, it is known that, upon irradiation with light from ultraviolet rays to visible light, a polymer having vinyl groups undergoes a crosslinking reaction due to addition reactions of the double bond, cis-trans isomerization reactions and the reaction with oxygen, though the type of reaction varies depending upon the structure of the polymer.
The present inventors found that, when a film of a poly(arylenevinylene) polymer of the formula (I) is irradiated with light such as that from a xenon lamp, the fluorescence intensity of the portion irradiated with light decreases in stages depending upon the light irradiation time and the light intensity used in the light irradiation. By utilizing the above finding, a difference in the fluorescence intensity between a light-irradiated portion and a light-unirradiated portion can be easily established on the film of poly(arylenevinylene) polymer. Thus, according to the present invention, it is possible to provide a poly(arylenevinylene) polymer film having a pattern of the desired fluorescence intensity as well as an organic electroluminescent device using such a patterned film of poly(arylenevinylene) polymer.
The poly(arylenevinylene) polymer according to the present invention is represented by the following general formula (I):
xe2x80x94(Arxe2x80x94CR1=CR2)nxe2x80x94xe2x80x83xe2x80x83(1)
wherein Ar is a substituted or unsubstituted divalent aromatic hydrocarbon group or a substituted or unsubstituted divalent heterocyclic ring group, and the aromatic hydrocarbon group and the heterocyclic ring group may be a fused ring, R1, R2 independently of each other, are H, CN, alkyl, alkoxy are substituted or unsubstituted aromatic hydrocarbon groups or substituted or unsubstituted aromatic heterocycles, which may both be fused rings, and n is an integer of 2 or more. It is preferred that either R1 or R2 is H and more preferred that both R1 and R2 are H.
There is no specific limitation in xe2x80x9cnxe2x80x9d as long as it is an integer of 2 or more, but n is preferably from 5 to 30,000, and more preferably from 10 to 10,000.